Infusion apparatus

ABSTRACT

Infusion apparatus is provided for discriminating the specifications of syringes of any manufacturer, setting alarm levels corresponding to contained liquid solutions having various viscosities, and obtaining a net pressure for infusion from the force to a plunger by considering pressure loss dependent on a friction factor between the barrel and the plunger of the syringe. Syringe diameter is detected digitally to determine a capacity signal. The plunger force is detected by a pressure sensor and then A/D converted to a digital pressure signal. Specifications of syringes of manufacturers based on the syringe capacity signal are compared with the signals of the mounted syringe to select one among operation programs corresponding to their syringe specifications. A Dip switch selects a group of the operation programs for manufacturers. The digital pressure signal from the pressure converter is input to a comparator through a subtracter cooperating with a pressure loss constant table to compare outputs from a supremum constant table indicating the needle for the infusion solution is correctly injected into the blood vessel or muscle of the patient. A pressure loss is subtracted from the force detected based on the friction factor and the output from the pressure converter produces a value corresponding to the net pressure.

TECHNICAL FIELD

The present invention relates to an infusion apparatus for injectingvarious types of medicinal solutions or blood into a human body by usinga syringe type injection pump.

BACKGROUND ART

Infusion apparatuses, e.g., pumps, for automatically performing infusionby using syringes are conventionally known. A medicinal solution in amedicine bottle is drawn into the syringe through a needle.Alternatively, a medicine cartridge is stored in the syringe. After thesyringe containing the medicinal solution is mounted on the pump, asyringe plunger is pushed by a slider of the pump at a constant rate, sothat the infusion solution is automatically administered to the patient.Infusion apparatuses of this type are disclosed in JP-A-48-62289,JP-U-57-76637, and JP-B-63-443390.

In such an infusion apparatus, a medicinal solution or blood must bereliably injected at a predetermined flow rate to the patient without anabnormality. Thus, in the conventional infusion apparatus, a slider forpushing the plunger is controlled by using, e.g., a microcomputersystem. In another conventional infusion apparatus, the supremumpressure at the needle is determined immediately before the medicinalsolution is injected to the patient. The force to the plunger is thenexpected and calculated at the supremum. An alarm is produced or theoperation of the pump is stopped when this supremum force is detected.

syringes used in the infusion apparatus are manufactured by variousmanufacturers. Their sizes or configurations are standardized to acertain degree. However, the syringes of different manufacturers havedifferent inherent slidable or dynamic frictional resistance values.Accordingly, it needs various specification data, e.g., the slidablefrictional resistance, stroke, and capacity of the syringes. The variousspecification data therefore can be stored by using an EPROM or thelike. When data on the slidable frictional resistance of the syringe ofa certain manufacturer is stored in the EPROM of one infusion apparatus,its apparatus adapts to that of the syringes according to thespecifications of the manufacturer.

In the conventional infusion apparatus, however, even when the force tothe plunger exceeds the supremum force to produce the alarm, sometimesno abnormality occurs. This is because injecting pressure changes arenot considered, which depend on the viscosity of the medicinal solution,the needle gauge or size, and the injecting location (vein, artery ormuscle) of the patient. More specifically, since the supremum force isset according to a medicinal solution having a low viscosity, it doesnot correspond to a high-calorie medicinal solution having a highviscosity that attracts attention lately. Also, the supremum force doesnot correspond to a reaction against the injecting pressure when aneedle having a small gauge and thus a large pressure loss is used, andwhen injection into an artery is performed, which are influenced by theblood pressure. In a worst case, when the patient takes a sudden turnfor the worse and the blood pressure is increased, infusion is sometimesstopped by an alarm.

Also, in the conventional infusion apparatus, an alarm is sometimesproduced before the force to the plunger reaches a predeterminedsupremum, and the operating pump is stopped. This is because thefriction factor between the barrel and the plunger is not considered.More specifically, to determine the net injection amount of the infusionsolution from the force to the plunger, it is indispensable to considerthe friction factor between the barrel and the plunger slidably mountedthereto.

Furthermore, since the conventional infusion apparatus employs a smallcapacity EPROM, it cannot store all the specification data of thesyringes of different manufacturers and all the operation programs foruse in these syringes. Therefore, different standard EPROMs fordifferent manufacturers must be used. Hence, a label must be adhered tothe infusion apparatus to indicate that this apparatus corresponds tothe syringe of a specific manufacturer, thereby clarifying the syringeof which manufacturer can be used in this infusion apparatus. If asyringe of a manufacturer to which the infusion apparatus does notcorrespond is erroneously used, problems occur because the specificationdata of the syringe is different. Then, a medicinal solution cannot besupplied at a preset flow rate. Various types of alarm units providedfor safety infusion operation are malfunctioned.

The present invention, made in view of the above situations, has as itsobject to provide an infusion apparatus for obtaining a net pressure forinfusion from the force to a plunger by considering the friction factorbetween the syringe barrel and the plunger.

It is another object of the present invention to provide an infusionapparatus capable of switching the alarm level of the injection pressureover a plurality of levels by considering reactions caused by theviscosity of the medicinal solution, the gauge of the needle, and theinjecting location (vein, artery or muscle) of the patient.

It is still another object of the present invention to provide a highlyreliable, simple infusion apparatus which can reliably correspond tosyringes, and inject a medicinal solution at a preset flow rate to thepatient even when these syringes having various specifications are used.

An infusion apparatus according to the present invention comprises asyringe for storing a medicinal solution, driving means for pushing aplunger in the syringe barrel at a predetermined speed, a pressuresensor for detecting a force to the plunger, a comparator capable ofreceiving an output from the pressure sensor, supremum and lowest limitconstant tables each connected to inputs of the comparator, and aselection switch for selecting supremum and lowest limit values outputfrom the supremum and lowest limit constant tables. A signal from thepressure sensor or an analog signal is A/D converted into, e.g., an8-bit digital signal by a pressure converter.

According to another embodiment, an apparatus may further comprise alearning function of updating the supremum and lowest limit valuescorresponding to an alarm produced within a predetermined period afterinfusion is started.

An infusion apparatus according to another embodiment comprises asyringe for storing a medicinal solution, driving means for pushing aplunger into the syringe barrel at a predetermined speed, a pressuresensor for detecting a force to the plunger, a pressure converterconnected to a signal output from the pressure sensor, a pressure lossconstant table for outputting a pressure loss based on a friction factorbetween the barrel and the plunger, and a subtracter for subtracting thepressure loss from a detected force output from the pressure converterto obtain a net pressure.

According to still another embodiment, an apparatus may further comprisea learning function of storing, as the pressure loss, a force obtainedwhen the plunger in the empty syringe is pushed at the predeterminedspeed, in the pressure loss constant table in a RAM. The friction factoris determined based on the standards and manufacturer specifications ofthe syringe. Accordingly, various values are stored in the ROM.

An infusion apparatus according to this still another embodiment of thepresent invention, in which a movable slider is abutted on a syringeplunger, and the plunger is pushed by moving the slider, comprisesdriving means for pushing the slider at a predetermined speed, means fordetecting a force to the plunger, syringe diameter means for detecting acapacity of the syringe, data storage means for storing specificationdata for various syringes, program storage means for storing operationprograms for said various syringes, comparing means for comparinginformation output from the pressure sensor and the syringe diametermeans, with the specification data of the syringes stored in the storagemeans to determine a specific syringe to be mounted, and switching meansfor selecting a predetermined operation program for said specificsyringe among the operation programs stored in the program storage meansaccording to a comparison result of the comparing means.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing the outer appearance of an infusionapparatus according to an embodiment of the present invention.

FIG. 2 is a partially cutaway sectional view of the infusion apparatusshown in FIG. 1.

FIG. 3 is a sectional view showing a syringe diameter means fordetecting the capacity of a syringe.

FIG. 4 is a block diagram schematically showing the infusion apparatusaccording to the first embodiment of the present invention.

FIG. 5 is a block diagram schematically showing an infusion apparatusaccording to the second embodiment of the present invention.

FIG. 6 is a block diagram schematically showing an infusion apparatusaccording to the third embodiment of the present invention.

BEST MODE OF CARRYING OUT THE INVENTION

Preferred embodiments of an infusion apparatus according to the presentinvention will be described with reference to the accompanying drawings.

FIG. 1 shows the outer appearance of an infusion apparatus 1 accordingto an embodiment of the present invention. Provided on a case 2 of theinfusion apparatus 1 are an operating section 4 for monitoring theinfusion operation of a syringe 3 and the infusion state of the syringe3, and a mount section 5 on which the syringe 3 can be mounted. As thesyringe 3, a standard product having a total capacity of, e.g., 10 mm,20 mm, 30 mm, or 50 mm is used according to the application. Thus, thesyringe 3 has an outer diameter corresponding to the standard. Standard50-ml syringes 3 of different manufacturers have different coefficientsof friction with respect to the plunger, and have different pressuresper unit flow rate. However, syringes of the same standard manufacturedby the same manufacturer have substantially no variation in frictionfactor, and thus have a substantially constant friction factor.

A capacity indicator 6, a centralized indicator 7, an infusion startindicator 8, an infusion stop indicator 9, and a four-digit numericalindicator 10 are disposed on the operating section 4. The capacityindicator 6 indicates the size of the mounted syringe 3 by, e.g., anLED. The centralized indicator 7 indicates various operating states. Thenumerical indicator 10 indicates the flow rate, accumulated flow rate,or one-shot flow rate during infusion by a unit of ml/hr (time) or ml.

Thus, the centralized indicator 7 has a test or self-diagnosticindicator, an automatic alarm level set indicator, and a clogging/openindicator. The self-diagnostic indicator indicates a self-diagnosticprogram run. The automatic alarm level set indicator is turned on for apredetermined period, after infusion is started, to indicate that thesupremum and lowest limit alarm values are updated. The clogging/openindicator is turned on when an abnormality occurs during infusion, e.g.,when the needle is clogged or accidentally removed after thepredetermined period elapses. The centralized indicator 7 also has alow-voltage indicator, an erroneous operation indicator, an infusioncompletion indicator, and a stand-by indicator. The low-voltageindicator indicates that an incorporated secondary cell reaches its uselimit. The erroneous operation indicator indicates an erroneousoperation sequence. The infusion completion indicator indicatescompletion of infusion. The stand-by indicator indicates that completionof infusion is within one minute.

In addition, a one-shot button 11, an infusion amount button 12, aninfusion start/stop button 13, a fast-feed button 14, and a power supplybutton 15 are disposed on the operating section 4. The one-shot button 1can feed a larger amount of infusion solution than an ordinary infusionamount when an emergency occurs. The infusion amount button 12 is usedto select the indicated content of the numerical indicator 10.Furthermore, flow rate set buttons 16 for setting the flow rate in unitsof digits are disposed above and under the numerical indicator 10. Theflow rate set buttons 16 can be set to 0.0 to 199.9 ml/hour. A learningfunction set button 17 or buzzer stop button (not shown) is alsodisposed on the operating section 4. When the plunger in the emptysyringe 3 is pushed at a constant speed, the pressure of this time isregarded as the pressure loss and stored in a pressure loss constanttable by the operation of the learning function set button 17 or buzzerstop button.

Referring to FIG. 2, the mount section 5 includes a rest portion 22 onwhich a barrel 21 of the syringe 3 is placed. A plunger 23 slidablymovable in the barrel 21 can be pushed by a slider 24. A driving means25 transports the slider 24 toward the rest portion 22 (in a directionof an arrow a) while supporting it. A holder 26 for fixing the placedsyringe 3 from above is formed on the rest portion 22. A syringediameter detector 27 is disposed under the holder 26. A release button28 for releasing the driving means 25 and restoring the slider 24 to theinitial position is provided to the slider 24. Part of the driving means25 is covered with a bellows 29 so that the interior of the drivingmeans 25 cannot be seen.

Accordingly, in the pump having the syringe 3, the barrel 21 is held bythe holder 26 and the rear end portion of the plunger 23 is abutted tothe slider 24. A flexible infusion pipe (not shown) communicating withthe needle is connected to the distal end of the syringe 3. Hence, whenthe syringe 3 is mounted on the rest portion 22 and the slider 24 iscaused by the driving means 25 to push the plunger 23 at a predeterminedspeed in the direction of the arrow a, the medicinal solution in thesyringe 3 is pushed out at a predetermined flow rate, and injected tothe patient through the infusion pipe and the needle.

FIG. 2 also shows the driving means 25 of the slider 24 and a pressuresensor 40 for detecting a pressure obtained when the medicinal solutionis injected to the patient. The driving means 25 has a main shaft 30slidably supported in the mount section 5, and a release shaft slidablysupported in the mount section 5 and parallel to the main shaft 30. Oneend of the main shaft 30 is fixed to the slider 24, and the other endthereof is fixed to an engaging member 32. The release shaft is not seenbecause of disposing behind the main shaft 30. The release shaft has oneend portion axially supported by the slider 24, the other end portionaxially supported by the engaging member 32, one end fixed to therelease button 28 through an arm, and the other end fixed to theengaging pawl (not shown) of the engaging member.

The engaging member 32 is slidably supported in the mount section 5 andreciprocally moved by a feed screw 34, engageable with the engagingpawl, in the same manner as the slider 24. More specifically, theengaging member 32 is slidably mounted on a guide rod and the feed screw34 that are disposed parallel to the main shaft 30 and the release shaftin the mount section 5. The feed screw 34 is axially supported in themount section 5 to be slightly movable in the axial direction. The guiderod (not shown) is disposed in front of the feed screw 34. Since theengaging member 32 and the slider 24 are slidably supported in the mountsection 5 by the release rod and the feed screw 34, the guide rod can beeliminated.

FIG. 3 shows the syringe diameter means 27 for detecting the capacity ofthe syringe 3. Syringes 3 used in this infusion apparatus aremanufactured by various manufacturers, but the diameter of the syringe 3corresponding to the capacity of the syringe 3 is determined bystandards. Accordingly, syringes 3 having the same capacity have thesame diameter even if they are manufactured by different manufacturers.

The syringe diameter means 27 includes a coupling shaft 51, a mountmember 52, a blocking plate 53, and a plurality of opto-couplers 55. Thecoupling shaft 51 is vertically moved in the interlocked manner to theholder 26 that holds the barrel 21 of the syringe 3. The mount member 52is provided under the coupling shaft 51 and serves to mount the blockingplate. The blocking plate 53 has notches. Each opto-coupler 55 comprisesan LED, a photodetector and a groove corresponding to the blocking plate53. The holder 26 is biased downward by a spring 54.

In this case, three or upper, middle and lower photointerrupters oropto-coupler 55 are used to detect four syringes 3 each having differentcapacity. FIG. 3 shows barrels 21 of a 50-ml syringe 3, a 30-ml syringe,a 20-ml syringe, and a 10-ml syringe with solid, dot-dash, dot-dot-dashand broken lines, respectively. A plurality of notches are formed in theblocking plate 53. The widths of the notches are determined such thatthe photodetector of the lower opto-coupler 55 is exposed upon mountingthe 50-ml syringe 3; all the three photodetectors thereof are shieldedby the plate 53 upon mounting the 30-ml syringe 3; the upperphotodetector is exposed upon mounting the 20-ml syringe 3; and theupper and middle photodetectors among the three opto-couplers 55 areexposed upon mounting the 10-ml syringe 3. When a syringe 3 is notmounted, all the photodetectors of the three opto-couplers 55 areexposed. In this manner, information representing the capacity andpresence/absence of the syringe 3 is output from the syringe diametermeans 27.

Alternatively, the widths of the notches of the blocking plate 53 may beset such that all the photodetectors are shielded when any syringe isnot mounted; only the lower photodetector (001) is exposed when the10-ml syringe 3 is mounted; the middle and lower photodetectors (011)are shielded when the 20-ml syringe 3 is mounted; all the photodetectors(111) are exposed when the 30-ml syringe 3 is mounted; and only thelower photodetector (110) is shielded when the 50-ml syringe 3 ismounted. Accordingly, the syringe diameter detector 27 has a decoder forreceiving a 3-bit wide digital signal from the three photodetectors, anddecoding its digital signal into a 1-bit signal representingpresence/absence of the syringe and a 2-bit diameter signal Rrepresenting the type of the syringe and outputting them.

Referring again to FIG. 2, the feed screw 34 has one end 34a mounted ona pressure sensor 40 through a hard ball, and the other end fixed to agear wheel 41 of a reduction gear mechanism. The gear wheel 41 mesheswith a pinion. As shown in FIG. 4, under the control of a motor controlcircuit 43, a motor 42 having a rotating shaft fixed to the pinion isrotated at a preset speed by a flow rate signal sent from the flow rateset buttons 16 and the diameter signal R. The flow rate signal and thediameter signal R are stored in a memory or RAM.

The slider 24 is moved by the feed screw 34, driven based on the presetflow rate, to push the plunger 23 of the syringe 3 in the direction ofthe arrow a, thereby pushing out a medicinal solution at a predeterminedflow rate. The reaction of the pushing force of the slider 24 on theplunger 23 is transmitted to the feed screw 34 through the couplingmember 30 and the driven member 32, and the pressure sensor 40electrically converts this reaction into a pressure signal and outputsit.

FIG. 4 is a block diagram of the infusion apparatus according to thefirst embodiment of the present invention. The infusion apparatus 1determines the infusion state based on the pressure signal output fromits pressure sensor 40, and performs control to stop infusion. Thepressure signal output from the pressure sensor 40 is amplified by anamplifier and input to a pressure converter 44.

A ROM (data storage means) 46 stores specification data of syringesmanufactured by various manufacturers. A program storage means 68 storesoperation programs corresponding to the syringes manufactured by thevarious manufacturers. For example, an operation program correspondingto a syringe available from a manufacturer A is stored in a program area68a. Another operation program corresponding to a syringe available froma manufacturer B is stored in a program area 68b.

A Dip switch 65 serves to perform an initial setup operation of thesyringe employed in the infusion apparatus. According to the setupoperation by the Dip switch 65, a CPU 66 selects an operation programstored in the program storage means 68. For example, when a setupoperation is performed by the Dip switch 65 to use the syringe availablefrom the manufacturer A, the CPU 66 selects the program area 68a storingthe operation program corresponding to the syringe of the manufacturerA.

In response to the setup operation by the Dip switch 65, the ROM 46outputs predetermined specification data from stored specification dataof the syringes manufactured by the various manufacturers.

When a syringe is placed and the infusion apparatus is operated, thesyringe diameter means 27 detects the capacity of the syringe, and themotor control circuit 43 outputs a control signal to the motor 42 sothat infusion is performed at a preset flow rate. Upon start ofinfusion, the pressure sensor 40 detects the force to the plunger orinner-pressure of the infusion solution and outputs a detected pressuresignal to the pressure converter 44. The pressure converter 44 outputsvarious types of information signals to a comparator 47 based on thesignals obtained from the pressure sensor 40 and the syringe diametermeans 27. The ROM 46 outputs the specification data of the syringe tothe comparator 47, and the comparator 47 compares information outputfrom the pressure converter 44 with information output from the ROM 46.

When a predetermined syringe is mounted on the infusion apparatus and atest or self-diagnostic operation is performed, the slider starts movingto push the plunger. Information on the slidable frictional resistanceand the like of the syringe obtained at this time and data stored in theROM (data storage means) 46 are compared by the comparator 47. If thecomparison result is correct, the operation of the infusion apparatuscan be continued. When a syringe having specifications different fromthose of the initially set syringe is mounted on the infusion apparatusand a test operation is performed, the slider starts moving to push theplunger, in the same manner as the test operation described above.Information on the slidable frictional resistance and the like of thesyringe obtained at this time and data stored in the ROM 46 are comparedby the comparator 47. If the comparison result is determined to beincorrect, the operation of the infusion apparatus is automaticallyinterrupted.

If an alarm sound is produced at this time, the operator of the infusionapparatus notices the erroneous operation. Alternatively, a coded errormessage may be indicated by using the numerical indicator 10 shown inFIG. 1. For example, when a syringe of the manufacturer B is mounted onan infusion apparatus preset to correspond to a syringe of themanufacturer A, the infusion apparatus produces an alarm sound to informthe operator of this fact. The operator recognizes the erroneousoperation and performs a correct operation. For example, if a syringe ofthe manufacturer A is available at hand, he may mount it on the infusionapparatus. If only the syringe of the manufacturer B is available athand, he may operate the Dip switch 65 to change the initial setting ofthe infusion apparatus to select the program area 68b storing theoperation program corresponding to the syringe of the manufacturer B andstored in the program storage means 68.

According to the infusion apparatus of the present invention, thespecification data of syringe having various specifications manufacturedby various manufacturers are stored in the ROM 46. Hence, by switchingthe Dip switch 6 5 to designate change of the initial setup, operationprograms stored in the program storage means 68 and corresponding tosyringes having various specifications are selected, and predeterminedspecification data of the specification data of the syringes havingvarious specifications stored in the ROM 46 are selected.

When the test operation is performed, the specifications of the mountedsyringe and the specification data of the syringes having variousspecifications stored in the ROM 46 may be compared to discriminate thespecifications of the mounted syringe. Then, an operation programcapable of corresponding to a specific one of the syringes havingvarious specifications stored in the program storage means 68 may beautomatically selected by a pointer 67.

The infusion apparatus according to the first embodiment of the presentinvention has a ROM (data storage means) for storing the specificationdata of the syringe have various specifications that can be mounted.Hence, the ROM need not be exchanged for causing the infusion apparatusto correspond to syringes having various specifications. Since theinitial setup can be changed by the Dip switch, even when a syringedifferent from an initially set syringe is mounted, it can be coped withby only switching the Dip switch. Furthermore, the specification datastored in the ROM and the data of the mounted syringe are compared bythe comparator to determine the specifications of this syringe. Then, apredetermined operation program of the operation programs stored in theprogram storage means can be automatically selected by the pointer.

FIG. 5 shows an infusion apparatus according to the second embodiment ofthe present invention. Referring to FIG. 5, members corresponding tothose shown in FIG. 4 are denoted by the same reference numerals, and adetailed description of the corresponding members will be omitted.

A pressure signal output from a pressure sensor 40 is amplified by anamplifier and input to a pressure converter 44. After A/D conversion,the pressure converter 44 converts the pressure difference caused by adifference in syringe diameter based on a 2-bit diameter signal R,thereby obtaining a pressure per unit area of the medicinal solution. Anoutput from the pressure converter 44 is input to a subtracter 45.

The subtracter 45 also receives an output from a pressure loss constanttable 46 which outputs a pressure loss based on a friction factorbetween a barrel 22 and a plunger 23. The pressure loss constant table46 has a ROM 49 for receiving, e.g., a 3-bit manufacturer signal Moutput from a syringe type selection switch 48. For example, the 2-bitdiameter signal R corresponding to four different syringe diameters isinput to the ROM 49. Then, a pressure loss corresponding to a syringehaving a specific diameter, currently in use, of a specific manufactureris input to the subtracter 45. Accordingly, a value concerning thefriction factor to be stored in the ROM 49 is determined based on thestandards and manufacturer specifications of the syringe 3.

In this another embodiment, a learning function is provided. Accordingto this function, a pressure obtained when the plunger 23 in the emptysyringe 3 is pushed at a constant speed is stored as a pressure loss inthe pressure loss constant table 46. In this case, the pressure lossconstant table 46 usually has a RAM or register 50 for storing theinitial pressure value dependant on the friction factor obtained whenthe plunger 23 in the empty syringe 3 is pushed.

This learning function is effective in a case wherein the hospitalusually uses the syringe 3 of a specific appointed manufacturer and asyringe 3 of another manufacturer must be used because of an emergencyor of an inappropriate stock management. Accordingly, this learningfunction is practiced upon shipping from the factory if the hospital towhich the syringes 3 are supplied is known in advance, or is practicedwhen the appointed manufacturer is changed by the hospital.

The output from the pressure loss constant table 46 is also input to thesubtracter 45 and subtracted from the pressure value obtained uponinjection, thereby obtaining a net pressure. This net pressure signal isoutput to a comparator 47 to prevent an adverse influence caused by thefriction factor of the plunger 23 in the syringe 3. Alternatively, thepressure loss constant table 46 may have a learning function RAM orregister 50 for storing a pressure value obtained when the plunger 23 inthe empty syringe 3 is pushed at a constant speed.

The comparator 47 receives a clogging state detecting supremum value 71indicating whether the needle for the infusion solution is correctlyinjected into the blood vessel or muscle of the patient, and an openstate detecting lowest limit value 72 indicating whether the needle oran infusion pipe is removed by an external factor, e.g., when thepatient turns over in the bed, and compares them with the net pressuresignal. When these supremum and lowest limit values are digital values,they are supplied from the Dip switch or the ROM by the operation of aclogging pressure level selection switch 73, and changed according tothe diameter signal R and the viscosity of the infusion solution.

When the pressure signal falls outside the range of the supremum andlowest limit values, the comparator 47 detects a corresponding abnormalstate, and inputs an alarm signal to an alarm circuit 74. The alarmcircuit 74 indicates an abnormal state on the clogging/open indicator 7of FIG. 1 and supplies a stop signal ST to a motor control circuit 43 tostop a motor. Hence, the infusion state can always be monitored.

The alarm circuit 74 outputs alarm signals having various contents. Forexample, when a used syringe 3 is replaced with a fresh syringe 3containing a new medicinal solution, the diameter of the used syringe 3stored in advance and the diameter of the fresh syringe 3 are compared.If the comparison result is different, an alarm is produced. The alarmcan be indicated in the form of sound, light, or the like depending onits contents. The respective circuits in FIG. 2 can be constituted byanalog circuits, and a pulse motor can be used as the motor.

As described above, according the infusion apparatus of the secondembodiment of the present invention, since a pressure loss constanttable or a learning function considering the friction factor between thesyringe barrel and the plunger is used, an accurate net pressure can bedetected, a solution injection amount can be precisely detected, and anabnormality during infusion, e.g., removal of the needle or tube, andclogging of the needle, can be appropriately detected, so that safeinfusion can always be performed.

FIG. 6 shows an infusion apparatus according to the third embodiment ofthe present invention. Referring to FIG. 6, members corresponding tothose shown in FIG. 5 are denoted by the same reference numerals, and adetailed description of the corresponding members will be omitted.

A comparator 47 receives an output from a clogging state detectingsupremum constant table 71 indicating whether the needle for theinfusion solution is correctly injected into the blood vessel or muscleof the patient, and an output from an open state detecting lowest limitconstant table 72 indicating whether the needle or an infusion pipe isremoved by an external factor, e.g., when the patient turns over in thebed, and compares them with the net pressure signal.

The supremum and lowest limit constant tables 71 and 72 are ROMs or RAMsselected by a clogging pressure level selection switch 73 or a selectionregister. The clogging pressure level selection switch 73 outputsappropriate supremum and lowest limit values stored in the supremum andlowest limit constant tables according to the viscosity of the infusionsolution, and is usually incorporated in the body so that it cannot beeasily operated. The selection switch 73 can be manually operated by,e.g., a nurse to set, e.g., 16 alarm levels according to the gauge ofthe needle and the injecting location of the patient.

According to this another embodiment, when the needle is accuratelyinserted in the injecting location of the patient, the alarm level canbe automatically set by using the fact that injection of the infusionsolution reaches the stable state within a predetermined period, e.g.,one minute after injection of the infusion solution is started. Withinthe predetermined period after infusion is started, when the output fromthe comparator 47 reaches the alarm level, the contents of the registersof the supremum and lower constant tables 71 and 72 are updated toselect the alarm level of the next stage. Apparently, the learningfunction must monitor the condition of the patient under sufficientinfusion after the predetermined period elapses. This function updatesthe supremum and lowest limits corresponding to an alarm that can beproduced within the predetermined period after infusion is started.

The block circuit shown in FIG. 6 can use a one-chip microcomputersystem or an ordinary microcomputer system having a CPU, a ROM, a RAM,an I/O unit, an A/D converting function, and a D/A converting function.However, the block circuit can be constituted by an analog circuit. Inaddition, a pulse motor can be used as the motor.

As described above, according the infusion apparatus of the thirdembodiment of the present invention, since the alarm level of theinjection pressure is switched over a plurality of levels by consideringthe reaction caused by the viscosity of the medicinal solution, thegauge of the needle, and the injecting location (vein/artery/muscle) ofthe patient, alarm levels corresponding to infusion solutions havingvarious viscosities can be set. Based on the alarm level, an abnormalityduring infusion, e.g., removal of the needle or tube, and clogging ofthe tube can reliably be detected, thereby constantly performing safeinfusion.

What is claimed is:
 1. An infusion apparatus comprising:a syringe for storing a medicinal liquid solution between a barrel and a movable plunger; means for mounting said barrel on said infusion apparatus; driving means for pushing said plunger in said barrel at a predetermined speed; a pressure sensor for detecting the force on said plunger to provide an analogue signal; a pressure converter for receiving and A/D converting said analogue signal to a digital pressure signal; a comparator having inputs capable of receiving said digital pressure signal from said pressure converter; a supremum limit constant table having data outputs connected to other inputs of said comparator; and a selection switch for selecting a supremum limit value output from said supremum limit constant table.
 2. An infusion apparatus according to claim 1, further comprising a learning function of updating the supremum value corresponding to an alarm produced within a predetermined period after infusion is started.
 3. An infusion apparatus comprising:a disposable syringe for storing a medicinal liquid solution between a barrel and a movable plunger; means for mounting said barrel on said infusion apparatus; driving means for pushing said plunger in said barrel at a predetermined speed; a pressure sensor for detecting a force to said plunger to provide an analogue signal; a pressure converter for receiving and A/D converting said analogue signal to a digital pressure signal; a pressure loss constant table for outputting a pressure loss based on a friction factor between said barrel and said plunger; and a subtracter for subtracting the pressure loss from said digital pressure signal, thereby obtaining a net pressure to said plunger.
 4. An infusion apparatus according to claim 3, further comprising a learning function of storing, as the pressure loss, a pressure obtained when said plunger in said empty syringe is pushed at the predetermined speed, in said pressure loss constant table.
 5. An infusion apparatus according to claim 3, wherein the friction factor is determined based on standards and specifications of said syringe.
 6. An infusion apparatus in which a movable slider is brought into contact with a plunger of a syringe having a barrel, said barrel mounted on a base, and said plunger is pushed by moving said slider relative to said base, comprising:driving means for pushing said slider at a predetermined speed; a pressure sensor for detecting a force to said plunger to provide an analogue signal; a pressure converter for receiving and A/D converting said analogue signal to a digital pressure information; syringe diameter means for detecting the capacity of said plunger to provide digital diameter information; data storage means for storing specification data for various syringes; program storage means for storing operation programs for said various syringes; comparing means for comparing said information from said pressure sensor and said syringe diameter means, with the respective specification data of said syringes stored in said data storage means to determine a specific syringe to be mounted; and switching means for selecting a predetermined operation program for said specific syringe among said operation programs stored in the program storage means, according to a comparison result of said comparing means.
 7. An infusion apparatus comprising:a base; a disposable syringe having barrel and plunger between which a medicinal solution is contained; means for mounting said barrel on said base; a movable slider abutted to said plunger to push said plunger; a screw rod rotatably and axially-movably supported by said base and meshed with said movable slider; a motor for rotating said screw rod; and a pressure sensor disposed between an end of said screw rod and said base to provide an analogue signal corresponding to a force to said plunger.
 8. An infusion apparatus comprising:a base; a syringe having a movable plunger and a barrel detachably mounted on said base for storing a medicinal liquid solution; driving means fixed to said base for pushing said plunger at a predetermined speed; a pressure sensor associated with said drive means for detecting a force to said plunger to provide an analogue signal; an analogue to digital converter receiving and A/D converting said analogue signal to an n-bits wide digital pressure signal, where n is a positive integer; a comparator having n inputs capable of receiving said digital pressure signal; a supremum limit constant table having n outputs connected to other n inputs of said comparator; and a selector for selecting an address of said supremum limit constant table to provide a predetermined supremum limit constant value.
 9. An infusion apparatus in which a movable slider is brought into contact with a plunger of a syringe having a barrel, said barrel is mounted on a base, and said plunger is pushed by moving said slider relative to said base, comprising:syringe diameter means for detecting a capacity of said plunger to provide digital diameter information; data storage means for storing specification data of various types of syringes manufactured by various manufacturers; switching means for selecting predetermined specification data for said various syringes of a predetermined manufacturer among said various manufacturers; and comparing means for comparing said information from said syringe diameter means, with said respective specification data of said syringes to determine which syringe has been mounted on said base. 